Hydraulic fluids



Patented June 20, 1950 Charles W.

. HYDRAULIC-FLUIDS? Montgomery and William ,I. .Oakmont, and Robert E.Kline,. Pen nl Townslii'p, Allegheny. County, Pa.., a'ssi'gn'o'rsto GulfResearch [81" Development Company, Pittsburgh,

Pa., a corporation of Delaware f lonberi,

No Drawing. Application December 31, 1947,

. Serial No. 795,160

scams. (or 252.49)

This invention relates to hydraulic fluids, and 2 2 more particularly tofluids for use in hydraulically operated apparatus, such as brakemechanisms, fluid flywheels, shock absorbers, control mechanisms andsimilar hydraulically operated equipment. Various fluids have beenpreviously proposed for use in hydraulic systems as hydraulic powertransmission media or the like.

'In a great number of the previously proposed :fluids, there have beenmany disadvantages attendant to their use, such as corrosive anddeigrading efiects of such fluids on metal or rubber parts of thehydraulic equipment, a tendency to- Naphthenic acids occur in certaincrude oils, .notably those of the Gulf Coast regions, California,Roumania, and Venezuela. These materials may be recovered from the oilsin various ways, as known in the art. For example, crude oils may bedistilled over caustic soda 'or lime whereupon the soaps of thenaphthenic acids are retained in the stills along with tar and asphalticingredients. The soaps may then be recoveredfrom these materials bywashing with water, but difliculties are encountered with emulsions.Nevertheless, by using alcohol in the extraction, emulsions can beavoided and the acids recovered. The lighter acids are distilled overalongwith the oil distillates, and the naphthenic acids are removed fromthese with caustic soda more readily than from the heavy still bottomsbecause they are not contaminated with large amounts of pitch andasphalt. In separating the acids' from oils, one method is to wash theoils with dilute caustic soda, say 0.5 to 5%, at a temperature aboveabout 300 F., ordinarily not exceeding 500 F., and under a high pressuresuflicient at least to prevent evaporation -of the water. Under theseconditions the acids are neutralized and are removed in the aqueousliquor which separates cleanly from the oil while at the hightemperatures. The oil does not dissolve in the aqueous liquor to anyappreciable'extent and ii 66 the separation of the aqueous and oilylayers is effected hot, there is little hydrolysis of the soaps, so thatthe acid is substantially completely removed from the oil. The acids canthen be recovered by acidification of the soap solutions with a mineralacid, which releases the naphthenic acids. These are then decanted andmay be used as such, or they may be further purified, for example, byreconversion to soaps and reacidification or by distillation or similarprocesses.

Another method for recovering the acids consists in agitating a keroseneor gas oil distillate containing naphthenic acids with aqueous causticsoda, say 6 B., in an amount suflicient to neutralize all of the acid.The mixture is then allowed to settle for about 1 hour and the lower oraqueous layer is pumped ofi. The aqueous layer is then acidified withmineral acid,for examp1e,98 %"sulphuric acidfand' the n'ap'h-thenic acidseparates as an upperlayer, which is drawn oif and washed'with wateruntil-freepf mineral acid 7 v 1.

The products of these extractions,-which'are the well known naphthenicacids ofpomme'rce, are complex mixtures of acidic compounds containingat least one carboxyl groupingf No general chemicalstructure can as yetlee-given to this group of acids, since the structural analyses of onlya few have s'o'far been determine'du- Many of thecompounds appear to becharacterized by having in their molecular structur'one-br morerelatively saturated hydrocarbon rings; hence these extracted productsare considered"to be naphthem'c acids. It Would'seemthatthe highermolecular weight compounds contain polycyclic groupings. f Properties ofatypical naphthenic acid derived from petroleum'are shown in thefollowing table:

Analyticdl data for naphthenic'cc ids-used making'hydraulic fluids-'r-,1

naiinthenic acids GR7072 2 r i y, "API' Distillation Data at PercentDist.

10 mm., F. 760 mm., F.

In order to obtain the hydraulic fluidsoi our invention, the naphthenicacids as obtained above are esterified with an alcohol. to producesubstan tially neutral esters. The esteriflcation may be convenientlycarried out by refluxing 2 moles of an alcohol with 1 mole of thenaphthenic acid ior naphthenic acids or as selected fractions obtainedby fractional distillation.

Representative properties of some of the esters of this invention areshown in the following table:

ligiiliifig Viscosity at P Cut 5 3 s .Gr. Viscosity Na hthemcacid Ester11 8 API 0 Point p cot-mo 100F. 210F. Index r.

700 mm.) SUS sUs 1 359-580 23.1 0. 0153 59.9 .4 1 16 2 1 3 7 5.7 7.. 97"-30 n-OotylNaphthenate 4 410-422 22.2- 0.0200 33.0 38.4 98 -15 5422-431. 22. a 0. 9200 107 40. 0 9s .0 6 431-455 21.5 0. 0243 157 43.090 +30 1- 350-424 27. 0 0. 8804 02. 0 37. 3 +05 2' 424-420 27. 5- 0.8899 50.8- 30.4 115. +25 3 423-42; 2 g. g. 5 37. 7 119 +25 4 44+ 4 z 5.9 30.9 123 25 LBuYYlNaPhthenate-n- 5 7 450-458 25.5 0.9007 105 40.0 127I25 0 455-480 24. 0 0. 9047' 127 42. 8 123 +25 7 80-490 24. 0 0. 0005147 44. 3- 124 +40 s 490-504 24.5 0.9053 100 40.2 125 Composite 1-8350-504 25.5 0.5990 101 40.0 11% +35 1' 254 -503 22. 0 0. 9182 55. 1 53:s 02- -05 2 ggg ggg g .333; 33.1 30. s 20 3 80. 57.0 53 -05Z'EthYIHQXYLNaPhthe' 4 390'398 21.2- 0.0207 95.3 38.3 00 --05 Rate 5308-411. 21. 2. 0. 9207 39.0 59 -05 0 41 1 .22 21. 2 0. 9207 40. 0 5s-05 7 422-441 21.2 0. 9207- 152 42.3 71 -00 s 441-483 20. 5 0. 9300 23s47. 1 74 +55 Composite 1-8 254-483 21.4 0.9254 101 38.6 54 -05 fromabout 5 to 12 hours in the presence of a small amount of anhydroushydrogen chloride which, acts. as a catalyst. During this period wateris continuously removed from thereaction mixture until the theoreticalamount of separated water indicates that the reaction is complete, atwhich point the reaction is stopped. The excess alcohol is thendistilled from the crude product and the residue is recovered. Ifdesired theresiduemay be further purified by distilling under vacuum.Qther methods of esterification may be employed as willbe understood inthe art. Awide variety of alcohols may be employed for theesterification. Preferably these alcohols should be monohydric alcohols:containing up to 20 carbon atoms such as methyl, ethyl, propyl, butyl,amyl, hexyl, octyl, decyl, lauryl, myristyl, palm-ityl, eicosyl,isopropyl, z-ethyl-hexyl, allyl, crotonyl, oleyl propargyl,cyclohexanol, methylcyclohexanol, amylcyclohexanoh. phenylcyclohexanoL;cyclohexyl. cyclohcxanol, benzyl alcohol, phenylethyl alcohol,benzhydrol, tri-phenyl' carbinol, phenylpropyl' alcohol,phenylbenzylalcohol, naphthobenzyl alcoholgcinnamyl alcohol, furfurylalcohol, and tetrahydrofurfuryl alcohol. However, polyhydric alcoholsmay also be employed, such as vethylene glycol, propylene:- glycol,di-ethylene glycol, glycerol, and erythritol. Mixtures of any of theabove alcohols may also be employed,v particularly the mixturesof jalcohols obtained by the reduction of coconut oil fatty acids; themixture of higher molecular weight .alcohols obtained as. a.byaproductin thesynthesis of methanol from carbon monoxide and hydrogen;as well as the mixture of alcohols obvtainedas a by-product in thesynthesis. of. hysdizocarbons from carbon monoxide. and hydrogen.

The esters Of the naphthenic acids obtained as described hereinabovepresent a number of properties making them eminently suitable ashydraulic fluids. As seen from the, above table they possess arelatively high specific gravity; this property is very advantageousespecially in m0- mentum actuated hydraulic systems such as fluidflywheels. Furthermore the esters possess low volatility which meansthat at normal operating temperatures there will be practically no lossdue to evaporation and very little loss even at relatively highoperating temperatures.

In addition to the above characteristics these esters are susceptible tothe action of pour point depressants, and therefore can be made to-haveavery low pour point. For example, one per cent by weight of a known pourpoint depressant, such as the condensation products of chlorinated waxand phenol followed by further condensation 'of the reaction productwith organic acids, as exemplified by Santopour B which comprises thewax aryl' esters: of aromatic acids, will reduce the pour point of thelauryl ester from +45 F. to 5 F'. Other known pourpoint depressants suchas the. condensation products of chlorinated wax andnaphthalene may alsobe employed. In brief, the naphthenic acid esters present an aggregationof properties in a single material which render them particularlysuitable for general use as hydraulic fluids.

Although we have disclosed the use of the esters of the naphthenic acidsas hydraulic fluids by themselves, diluents and/or solvents may be addedto the ester to produce homogeneous hydraulic fluids. When a diluent isused it will ordinarily be present in. an amount from about 5 to 50% byweight of the esters of the naphthenic acids depending upon theparticular requirements, such as whether a light or a heavy grade offluid is required for a particular application. Although the esters ofthe naphthenic acids are soluble in a wide variety of solvents, it ispreferred to use relatively non-volatile solvents, as diluents of theesters in our hydraulic fluids. Typical classes of solvents which may beemployed as diluents are: 1) the glycol ethers including the monobutylether of ethylene glycol, the mono-ethyl ether of ethylene glycol, themethyl ether of ethylene glycol mono-acetate, the butyl ether ofdiethylene glycol and the diethyl ether of ethylene glycol; and (2)hydrocarbon solvents such as lightlubricating oils, gas oils, keroseneand the like.

The hydraulic fluids of the present invention, whether comprising theesters of the naphthenic acids alone or in combination with a pour pointdepressant or diluent as described above may be used as fluid power andtransmission media in any of the common hydraulic systems wherein poweris transmitted from an actuable element to an actuated element by meansof a fluid, the most common form of such a system comprising a pair ofvariable volume chambers with connecting conduit means, the chambers andthe conduit means being filled with a fluid hydraulic power transmissionmedium. The hydraulic fluids of the present invention may, of course,also be used in analogous equipment in which power transmission is notthe primary purpose of design, as for example in power absorptionsystems such as damping mechanisms, shock absorbers and the like.

In the following claims the expression naphthenic acids is employed toconnote the mixture of acids of that name currently obtained in thepetroleum refining industry, as well as naphthenic acid or acids whichare now being synthetically prepared.

What We claim is:

1. The process which comprises transmitting power by means of a liquidconsisting essentially of an ester of an alcohol and naphthenic acids.

2. The process of claim 1, wherein the alcohol is a monohydric alcohol.

3. The process of claim 1, wherein the alcohol is a monohydric alcoholcontaining up to 20 carbon atoms.

4. The process of claim 1, where in the alcohol is lauryl alcohol.

5. The process of claim 1, wherein the alcohol is n-octyl alcohol.

6. The process of claim 1, wherein the alcohol is 2-ethyl-hexyl alcohol.

7. The process of claim 1, wherein the liquid contains additionally apour point depressant.

8. The process of claim 1, wherein the liquid contains additionally fromabout 5 to per cent by weight of a relatively non-volatile liquiddiluent.

CHARLES W. MONTGOMERY. WILLIAM I. GILBERT. ROBERT E. KLINE.

REFERENCES CITED The following references are of record in the

1. THE PROCESS WHICH COMPRISES TRANSMITTING POWER BY MEANS OF A LIQUIDCONSISTING ESSENTIALLY OF AN ESTER OF AN ALCOHOL AND NAPHTHENIC ACIDS.